[Libav-user] [External] Questions about decoding broken streams

[Yurii Monakov]

Vasiliy, you can check AV_FRAME_FLAG_CORRUPT in AVFrame::flags and
FF_DECODE_ERROR_XXX bits in AVFrame::decode_error_flags.

Yurii

ср, 3 окт. 2018 г. в 17:37, Vasiliy Volkov <volk.vasiliy at gmail.com>:

> So there is no way to determine decoding errors except parsing log
> messages? It smells terrible )
> I see only way to detect such green images by analyzing color of decoded
> frames, but it can be CPU-intensive
>
> Also of course it's possible to patch some decoders, but It's also not
> correct way I guess.
>
> ср, 3 окт. 2018 г. в 13:48, Anton Shekhovtsov <shekh.anton at gmail.com>:
>
>>
>>
>> ср, 3 окт. 2018 г. в 13:31, Niraj Gandha <niraj.gandha at einfochips.com>:
>>
>>> Use below code and might help you in solving your problem.
>>>
>>> while (av_read_frame(refrenceFormatCtx, &packet) >= 0) {
>>>
>>> if (packet.stream_index == video_stream_index) { //packet is video
>>>
>>> if (stream == NULL) { //create stream in file
>>>
>>> stream = avformat_new_stream(output_ctx,
>>> refrenceFormatCtx->streams[video_stream_index]->codec->codec);
>>>
>>> avcodec_copy_context(stream->codec,
>>> refrenceFormatCtx->streams[video_stream_index]->codec);
>>>
>>> stream->sample_aspect_ratio =
>>> refrenceFormatCtx->streams[video_stream_index]->codec->sample_aspect_ratio;
>>>
>>> }
>>> int check = 0;
>>>  packet.stream_index = stream->id;
>>> int result = avcodec_decode_video2(codec_ctx, picture_yuv, &check,
>>> &packet);
>>>
>>> av_free_packet(&packet);
>>>
>>> av_packet_unref(&packet);
>>>
>>> if(result <= 0 || check == 0){
>>>
>>> continue;
>>>
>>> }
>>>
>>> if(initialize_rgb_requirements) {
>>>
>>> sizeofrgbpicture = avpicture_get_size(AV_PIX_FMT_RGB24,
>>> codec_ctx->width, codec_ctx->height);
>>>
>>> picture_rgb = av_frame_alloc();
>>>
>>> picture_buffer_rgb = (uint8_t*) (av_malloc(sizeofrgbpicture));
>>>
>>> avpicture_fill((AVPicture *) picture_rgb, picture_buffer_rgb,
>>> AV_PIX_FMT_RGB24, codec_ctx->width, codec_ctx->height);
>>>
>>> img_convert_ctx = sws_getContext(codec_ctx->width, codec_ctx->height,
>>> AV_PIX_FMT_YUV420P, codec_ctx->width, codec_ctx->height,AV_PIX_FMT_RGB24,
>>> SWS_BICUBIC, NULL, NULL, NULL);
>>> initialize_rgb_requirements=0;
>>>
>>> }
>>>
>>> int height = 0;
>>>
>>> if(picture_yuv->data != NULL) {
>>> height = sws_scale(img_convert_ctx, ((AVPicture*)picture_yuv)->data,
>>> ((AVPicture*)picture_yuv)->linesize, 0, codec_ctx->height,
>>> ((AVPicture*)picture_rgb)->data,((AVPicture*)picture_rgb)->linesize);
>>>
>>> }
>>>
>>> rgb_image_data = (uint8_t *)malloc(sizeofrgbpicture * sizeof(uint8_t));
>>>
>>> int ret = avpicture_layout((AVPicture *)picture_rgb, AV_PIX_FMT_RGB24,
>>> codec_ctx->width, codec_ctx->height, rgb_image_data, sizeofrgbpicture);
>>>
>>> emit imageQueued(rgb_image_data, codec_ctx->width,codec_ctx->height);
>>>
>>> }
>>> }
>>>
>>> Get Outlook for Android <https://aka.ms/ghei36>
>>>
>>> ------------------------------
>>> *From:* Libav-user <libav-user-bounces at ffmpeg.org> on behalf of Vasiliy
>>> Volkov <volk.vasiliy at gmail.com>
>>> *Sent:* Wednesday, October 3, 2018 3:44:49 PM
>>> *To:* libav-user at ffmpeg.org
>>> *Subject:* Re: [Libav-user] [External] Questions about decoding broken
>>> streams
>>>
>>> Well there is no anything unusual in our code. We're simply use this
>>> API:
>>> https://ffmpeg.org/doxygen/4.0/group__lavc__encdec.html
>>>
>>> avcodec_send_packet
>>> avcodec_receive_frame
>>>
>>> And for context we setup:
>>> context->err_recognition = AV_EF_EXPLODE | AV_EF_BITSTREAM |
>>> AV_EF_BUFFER | AV_EF_CAREFUL | AV_EF_COMPLIANT | AV_EF_AGGRESSIVE;
>>>
>>>
>>> ср, 3 окт. 2018 г. в 12:58, Niraj Gandha <niraj.gandha at einfochips.com>:
>>>
>>>> Hi Vasiliy,
>>>>
>>>> Can you share the code in which you are decoding the stream?
>>>>
>>>> Thanks,
>>>> Niraj Gandha
>>>>
>>>> Get Outlook for Android <https://aka.ms/ghei36>
>>>>
>>>> ------------------------------
>>>> *From:* Libav-user <libav-user-bounces at ffmpeg.org> on behalf of
>>>> Vasiliy Volkov <volk.vasiliy at gmail.com>
>>>> *Sent:* Wednesday, October 3, 2018 3:08:08 PM
>>>> *To:* libav-user at ffmpeg.org
>>>> *Subject:* [External] [Libav-user] Questions about decoding broken
>>>> streams
>>>>
>>>> CAUTION: This email originated from outside of the organization. Do
>>>> not click links or open attachments unless you recognize the sender and
>>>> know the content is safe.
>>>>
>>>> Hi,
>>>>
>>>> I'm trying to deal with broken streams with libav. Sometimes streams
>>>> can be broken due to nature of incoming network channel (UDP multicast) but
>>>> i'd like to "fix them" as much as possible. I'm trying to fill broken
>>>> frames with last good decoded frame. There are situations when I can do
>>>> such thing and everything is ok but most of time it's not helping: libav
>>>> tries to decode broken stream and add some green frames (h264 decoding)
>>>> which really catch your eyes when you watch this stream after encoding.
>>>> Is it possible to change this color to black for example? Can libav
>>>> while decoding set some flags to frames and mark them as broken or "green"?
>>>> It will be helpful because next I'll can replace such frames with
>>>> correctly decoded which fix it.
>>>>
>>>> Thanks
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>>
>>
>> What you wanted to show with this example? That's true, some (or all)
>> decoders don't return errors.
>> Example in ffv1dec.c
>>                 av_log(f->avctx, AV_LOG_ERROR, "CRC mismatch %X!", crc);
>> No error code returned from here. It is possible to abuse log hook
>> somehow.
>>
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